Melt spinning filtration bed retaining screen



T. L. CARTER 3,348,263

MELT SPINNING FILTRATION BED RETAINING SCREEN Oct. 24, 1967 Filed March 28, 1966 United States Patent ABSTRACT OF THE DISCLOSURE A spinneret assembly which includes an open top sand holder, with a sand retaining cap that extends above the top of the sand holder. The cap is a screen material that has a depending rim formed to fit inside the sand holder.

This invention relates generally to the production of yarns, filaments, ribbons and the like from synthetic linear polymers and more particularly to improvements in the assembly from which such articles are spun.

It is customary to filter a synthetic filament-forming composition before extruding it through a spinneret. Spinneret assemblies with filter beds which are typical of the prior art have been disclosed by Hull et al. in U.S. Patent 2,266,368 and by McGeorge in US. Patent 2,883,- 261. These assemblies include a holder filled with the filtering medium to a location near the top where a flat screen is placed to keep the top of the filtering medium level. As a practical matter, some space must be left at the top of the holder to allow for placement of the screen. In addition, a gasket is used between the holder and the spinning unit to maintain a tight pressure seal. The cumulative space which exists between the filtering medium and the spinning unit has been found detrimental to the spinning of light denier filaments in that a relatively stagnant pool of polymer exists in this space because of the low throughput required to spin these yarns. As a consequence, some of the polymer is exposed for more than a normal period of time to the process temperature and thermal degradation occurs with attendant formation of gel particles and gas bubbles. These products of degradation are detrimental to the spinning operation because if either a gel particle or a gas bubble reaches the spinneret opening a broken filament is likely to result.

According to the present invention, spinning performance is improved by using a spinneret assembly which includes an open top holder, a filter bed in the holder, parts for clamping the holder to an orificed surface of a spinning machine and a bed-containing cap for the holder. The cap has a central portion of screen material shaped complementally to the orificed surface and a depending rim portion fitted inside the holder. When the holder is clamped to the spinning machine, the central portion of the cap engages the orificed surface from which molten polymer is delivered to the spinneret assembly.

Various objectives and advantages will :be apparent from the following description wherein reference is made to the accompanying drawing in which:

FIGURE 1 is a fragmentary sectional view of a spinning machine and an operably associated spinneret as sembly;

FIG. 2 is a bottom view of FIG. 1;

FIG. 3 is an enlarged the sand holder; and

FIG. 4 is a perspective view of the sand-containing cap shown sectionally in FIGS. 1 and 3.

In FIGS. 1 and 2, the base portion of a spinning machine is represented by the numeral and has a supply port 12 in communication with a pump or other suitable the apparatus shown in fragmentary sectional 'view of 3,348,263 Patented Oct. 24, 1967 metering device by which molten material to be spun is brought to a spinneret assembly generally designated 14. As shown, base 10 has a cavity defined by a cylindrical side well, an upper surface 16 and intermittent shoulders 18 which support assembly 14.

As a component of assembly 14, open top holder 20 defines a chamber within which a filter bed 22 in the form of layers of sand or other finely divided inert material rests on a flat fine mesh screen 24. A spinneret plate 26 is fastened to the bottom of open top holder 20 by means of machine screws. Spinneret 2'6 and holder 20 are provided with aligned holes of sufiicient size and number to produce the'desired multifilament yarn. A ring 28 having a series of lugs 30 formed around its outer periphery is telescoped on operr top holder 20. In assembly, lugs 30 are inserted between shoulders 18 and then rotated to the illustrated location where they rest on the shoulders. Ring 28 is provided with threaded holes to receive bolts 32 which also pass through holes in a clamp ring 34 that abuts spinneret 26. A cap 36 of screen material has central and rim portions 38, 40 (FIGS. 3, 4). Portion 38 is flat and adapted for hearing engagement with orificed surface 16. Depending rim portion 40 is adapted for frictional engagement with the inside wall of holder 20. By means of a gasket 42, a sealed joint is secured when bolts 32 are tightened to force open top holder 20 and the gasket against surface 16 through the jacking force applied :by clamp ring 34 and lugs 30 acting against shoulders 18.

Referring to FIG. 3, central portion 38 of the cap screen is located a distance it above the open top holder 20. The distance it is slightly less than the thickness of gasket 42 to allow for compression. This relationship is critical only to the extent that It should not be less than the compressed thickness of gasket 42. Assembly 14 may be filled to the illustrated level by putting gasket 42 in place, filling open top holder 20 with inert granular material and depositing additional material to a level near the gasket top. Rim portion 40 of the cap screen is then inserted to a point where central portion 38 is just beneath the top of gasket 42. In this manner, when an assembly 14 is installed, the cap screen will be forced further into open top holder 20 as gasket 42 is compressed, thus insuring that the space between the open top holder 20 and the orificed surface 16 of base 10 will be completely filled. If it is not practicable to use a gasket in the filling operation, a jig of the same thickness may be used.

In FIG. 4, the cap screen is shown circular in form. Obviously, this is dependent on the shape of open top holder 20 which is often kidney-shaped or elliptical. The screen is made of stainless steel or other metallic or ceramic materials not reactive with the filament-forming composition and may vary from about 50 to 200 mesh in accordance with the yarn to be produced.

In actual runs, 40 denier, 10 filament, 6-6 nylon yarn has been spun from assemblies of the type shown herein and processed through the usual steps to packages. Comparative results indicate that elimination of open space between the filtering medium and the spinning machine leads to a reduction in total filament breaks. This worthwhile effact has been attributed to a reduction in the time of polymer exposure to elevated temperatures with attendant reductions in chemical decomposition and liberation of gaseous products that would form gas bubbles.

In addition to a reduction in filament breaks, the improved pack assembly offers process advantages. For example, the volume of filtering medium is increased so that a given spinneret assembly can remain in operation for longer periods of time. This is accomplished without extensive and costly modifications to the sand holder.

Though disclosed in connection with the manufacture of multifila-ment yarn from a synthetic linear polyamide,

3 the invention is obviously useful with other organic filament-forming compositions.

Many modifications and adaptations will be apparent to those skilled in the art without departing from the spirit of the invention, which is accordingly intended to be limited only by the scope of the appended claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a spinneret assembly including an open top holder, a filter bed in said holder and parts for clamping the open top of said holder to an orificed surface of a spinnin-g machine, a bed-containing cap for the holder,

said cap having a central portion of screen material shaped complementally to said surface and a depending rim portion fitted inside and extending upwardly beyond the open top of said holder, said cap being adapted to be forced into said holder when the open References Cited UNITED STATES PATENTS 2,266,368 12/1941 Hull et a1 188 2,732,585 1/1956 Wicker.

2,883,261 4/1959 McGeor-ge 188 X 3,006,028 10/1961 Calhoun 18-8 FOREIGN PATENTS 1,029,765 3/ 1953 France.

WILLIAM J. STEPHENSON, Primary Examiner. 

1. IN A SPINNERET ASSEMBLY INCLUDING AN OPEN TOP HOLDER, A FILTER BED IN SAID HOLDER AND PARTS FOR CLAMPING THE OPEN TOP OF SAID HOLDER TO AN ORIFICED SURFACE OF A SPINNING MACHINE, A BED-CONTAINING CAP FOR THE HOLDER, SAID CAP HAVING A CENTRAL PORTION OF SCREEN MATERIAL SHAPED COMPLEMENTALLY TO SAID SURFACE AND A DEPENDING RIM PORTION FITTED INSIDE AND EXTENDING UPWARDLY BEYOND THE OPEN TOP OF SAID HOLDER, SAID CAP BEING 